1. Field of the Invention
The present invention relates to a method of manufacturing a strained silicon-on-insulator (SSOI) substrate, and more particularly, to a substrate with an excellent surface micro-roughness required for enhancement of a device characteristic and a method of manufacturing an SSOI substrate that can separate a bonded substrate using a low temperature heat treatment.
2. Description of Related Art
T. A. Langdo, et al. published a paper in Solid-state electronics 48 (2004) regarding a method and characteristic of manufacturing a strained silicon-on-insulator (SSOI), titled “Strained Si on insulator technology: from materials to devices”.
The above technology initially grew a tilted silicon germanium (SiGe) layer on a silicon (Si) substrate, grew a relaxed SiGe layer on the tilted SiGe layer to contain a certain amount of germanium content, and then grew relaxed silicon on a top layer. Next, SSOI was manufactured by implanting ions into the relaxed SiGe layer, separating a bonded substrate from an ion implantation region of the relaxed SiGe layer after bonding with an oxidized silicon substrate and a thermal treatment thereof, and thereby forming a structure where a portion of the SiGe layer is left in the top layer, and removing the formed layer using diluted fluoride and a wet oxidation process at a temperature of less than or equal to about 800° C.
Also, U.S. patent application Ser. No. 6,992,025 B2 titled “Strained silicon-on-insulator from film transfer and relaxation by hydrogen implantation” discloses a method of manufacturing a strained silicon substrate by uniformly maintaining a germanium content when forming a SiGe layer on a silicon substrate, and then implanting hydrogen ions to thereby relax the SiGe layer, and growing strained Si. Next, in order to enhance the bonding strength when bonding the relaxed silicon substrate with an oxidized silicon substrate, a thermal treatment was performed for less than 14 hours at a temperature of about 250° C. and a bonded substrate was separated from an ion implantation region using thermal treatment for less than four hours at a temperature of about 400° C. Next, after a portion of the SiGe layer existing in the top layer was removed by dry etching, the thermal treatment was performed for less than one hour at a temperature of about 900° C. prior to chemical mechanical polishing (CMP) for enhancement of the surface roughness of the separated SiGe surface. Through the above process, an SSOI-structured substrate was finally manufactured by removing SiGe using wet etching.
The above-described technology relates to a separation and layer transfer technology using hydrogen ion implantation that implants ions into a strained silicon substrate among two substrates used for a manufacturing process and bonds the strained silicon substrate with an oxide substrate at room temperature. A layer transfer phenomenon corresponding to the ion implantation depth occurs in a bonded substrate via a predetermined process. A silicon oxide film and a transferred ion implantation layer, that is, a portion of SiGe and a strained Si layer exist on a single substrate. In this instance, a final SSOI-structured substrate may be provided by removing SiGe in the top layer.
In the above manufacturing process, separation and layer transfer technology using hydrogen ion implantation requires a relatively high temperature. Thus, a relatively long process time is required for raising, maintaining, and lowering the temperature. After the separation is completed, a characteristic value of the surface roughness is formed to be high. When the characteristic value of the surface roughness immediately after the separation is high, there may be a need for another process of removing SiGe and then improving the surface roughness. Accordingly, the process becomes complex, which may affect the movement of electrons and holes. Therefore, it may cause a mobility characteristic to be deteriorated when manufacturing a device.